Servo Feedback Control Based on Invisible Scanning Servo Beam in Scanning Beam Display Systems with Light-Emitting Screens

ABSTRACT

Scanning beam display systems that scan at least one invisible servo beam and an excitation beam onto a screen that emits visible light under excitation of the light of the excitation beam and control optical alignment of the excitation beam based on positioning of the servo beam on the screen via a feedback control.

BACKGROUND

This application relates to scanning-beam display systems.

In a scanning-beam display system, an optical beam can be scanned over ascreen to form images on the screen. Many display systems such as laserdisplay systems use a polygon scanner with multiple reflective facets toprovide horizontal scanning and a vertical scanning mirror such as agalvo-driven mirror to provide vertical scanning. In operation, onefacet of the polygon scanner scans one horizontal line as the polygonscanner spins to change the orientation and position of the facet andthe next facet scans the next horizontal line. The horizontal scanningand the vertical scanning are synchronized to each other to projectimages on the screen.

Such scanning-beam display systems can be in various configurations. Forexample, scanning-beam display systems may use passive screens that donot emit light but make light of the scanning beam visible to a viewerby one or a combination of mechanisms, such as optical reflection,optical diffusion, optical scattering and optical diffraction. Examplesof such displays include digital light processing (DLP) displays, liquidcrystal on silicon (LCOS) displays, and grating light valve (GLV)displays. Various front and rear projection displays use passivescreens. Scanning-beam display systems can also use active screens suchas fluorescent screens that include fluorescent materials to emitcolored light under optical excitation where the emitted light forms theimages visible to viewers. Examples of such display systems includecathode-ray tube (CRT) displays, plasma displays, liquid crystaldisplays (LCDs), light-emitting-diode (LED) displays (e.g., organic LEDdisplays), and field-emission displays (FEDs).

SUMMARY

The specification of this application describes, among others, displaysystems and devices based on scanning light on a screen. The describeddisplay systems use light-emitting screens under optical excitation andat least one excitation optical beam to excite one or morelight-emitting materials on a screen which emit light to form images.The fluorescent materials may include phosphor materials andnon-phosphor materials such as quantum dots. Servo control mechanismsfor such display systems are described. In some implementations,multiple lasers can be used to simultaneously scan multiple laser beamsto illuminate one screen. For example, the multiple laser beams canilluminate one screen segment at a time and sequentially scan multiplescreen segments to complete a full screen.

In one implementation, a scanning beam display system, includes anexcitation light source to produce at least one excitation beam havingoptical pulses that carry image information; a servo light source toproduce at least one servo beam at a servo beam wavelength that isinvisible; a beam scanning module to receive the excitation beam and theservo beam and to scan the excitation beam and the servo beam; and alight-emitting screen positioned to receive the scanning excitation beamand the servo beam. The screen includes a light-emitting area whichcomprises (1) parallel light-emitting stripes which absorb light of theexcitation beam to emit visible light to produce images carried by thescanning excitation beam, and (2) stripe dividers parallel to andspatially interleaved with the light-emitting stripes with each stripedivider being located between two adjacent stripes. Each stripe divideris optically reflective. An optical servo sensor is positioned toreceive light of the servo beam scanning on the screen including lightreflected by the stripe dividers and to produce a monitor signalindicative of positioning of the servo beam on the screen. This systemincludes a control unit operable to, in response to the positioning ofthe servo beam on the screen, adjust timing of the optical pulsescarried by the scanning excitation beam in response to the monitorsignal based on a relation between the servo beam and the excitationbeam to control the spatial alignment of spatial positions of theoptical pulses in the excitation beam on the screen.

In another implementation, a scanning beam display system includes alight-emitting screen comprising a light-emitting area which comprises(1) parallel light-emitting stripes which absorb excitation light toemit visible light, and (2) optically reflective stripe dividersparallel to and spatially interleaved with the light-emitting stripeswith each stripe divider being located between two adjacent stripes.Excitation lasers are provided to produce excitation laser beams of theexcitation light and at least one servo light source fixed in positionrelative to the excitation lasers is provided to produce at least oneservo beam at a servo beam wavelength that is invisible. This systemalso includes a beam scanning module to receive the excitation laserbeams and the servo beam and to scan the excitation laser beams and theservo beam; at least one first optical servo sensor positioned toreceive light of the servo beam reflected from the screen to produce afirst monitor signal indicative of positioning of the servo beam on thescreen; at least one second optical servo sensor positioned to receivelight of the excitation laser beams reflected from the screen to producea second monitor signal indicative of positioning of each excitationlaser beam on the screen; and a control unit operable to, in response tothe first and the second monitor signals, adjust timing of the opticalpulses carried by each excitation laser beam based on a relation betweenthe servo beam and each excitation laser beam to control the spatialalignment of spatial positions of the optical pulses in the excitationbeam on the screen.

In yet another implementation, a method for controlling a scanning beamdisplay system includes scanning at least one excitation beam modulatedwith optical pulses on a screen with parallel light-emitting stripes ina beam scanning direction perpendicular to the light-emitting stripes toexcite the fluorescent strips to emit visible light which forms images.The screen comprises stripe dividers parallel to and spatiallyinterleaved with the light-emitting stripes with each stripe dividerbeing located between two adjacent stripes and each stripe divider isoptically reflective. This method also includes: scanning a servo beam,which is invisible, along with the excitation beam on the screen;detecting light of the scanning servo beam from the screen includinglight produced by the stripe dividers to obtain a monitor signalindicative of positioning of the servo beam on the screen; and, inresponse to the positioning of the servo beam on the screen, adjustingtiming of the optical pulses carried by the scanning excitation beambased on a relation between the servo beam and the excitation beam tocontrol the spatial alignment of spatial positions of the optical pulsesin the excitation beam on the screen.

These and other examples and implementations are described in detail inthe drawings, the detailed description and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example scanning laser display system having alight-emitting screen made of laser-excitable light-emitting materials(e.g., phosphors) emitting colored lights under excitation of a scanninglaser beam that carries the image information to be displayed.

FIGS. 2A and 2B show one example screen structure with parallellight-emitting stripes and the structure of color pixels on the screenin FIG. 1.

FIG. 3 shows an example implementation of the laser display system inFIG. 1 in a pre-objective scanning configuration having multiple lasersthat direct multiple laser beams on the screen.

FIG. 4 shows an example implementation of a post-objective scanning beamdisplay system based on the laser display system in FIG. 1.

FIG. 5 shows one example for simultaneously scanning consecutive scanlines with multiple excitation laser beams and an invisible servo beam.

FIG. 5A shows a map of beam positions on the screen produced by a laserarray of thirty-six excitation lasers and one IR servo laser when avertical galvo scanner and a horizontal polygon scanner are at theirrespective null positions.

FIG. 6 shows one example of a scanning display system using a servofeedback control based on a scanning servo beam.

FIG. 7 shows an example of a servo detector for detecting the servofeedback light in FIG. 6.

FIGS. 8 and 9 show two screen examples for the servo control based on ascanning servo beam.

FIG. 10 shows optical power of servo light having optical signalscorresponding to stripe dividers on the screen.

FIG. 11 shows an example of a screen having peripheral reference markregions that include servo reference marks that produce feedback lightfor various servo control functions.

FIG. 12 shows a start of line reference mark in a peripheral referencemark region to provide a reference for the beginning of the activefluorescent area on the screen.

FIGS. 13 and 14 show optical power of servo light having optical signalscorresponding to stripe dividers, the start of line reference mark andend of line reference mark on the screen

FIGS. 15, 16 and 17 show examples of a use of a sampling clock signal tomeasure position data of stripe dividers on the screen using servofeedback light from the excitation beam or the servo beam.

FIG. 18A shows an example of a vertical beam position reference mark forthe screen in FIG. 11.

FIGS. 18B and 18C show a servo feedback control circuit and itsoperation in using the vertical beam position reference mark in FIG. 18Ato control the vertical beam position on the screen.

FIG. 19 shows an example of the screen in FIG. 11 having the start ofline reference mark and the vertical beam position reference marks.

FIG. 20 shows an operation of the servo control based on the servo beamthat is scanned with the excitation beam.

DETAILED DESCRIPTION

Examples of scanning beam display systems in this application usescreens with light-emitting materials or fluorescent materials to emitlight under optical excitation to produce images, including laser videodisplay systems. Various examples of screen designs with light-emittingor fluorescent materials can be used. In one implementation, forexample, three different color phosphors that are optically excitable bythe laser beam to respectively produce light in red, green, and bluecolors suitable for forming color images may be formed on the screen aspixel dots or repetitive red, green and blue phosphor stripes inparallel.

Phosphor materials are one type of fluorescent materials. Variousdescribed systems, devices and features in the examples that usephosphors as the fluorescent materials are applicable to displays withscreens made of other optically excitable, light-emitting, non-phosphorfluorescent materials. For example, quantum dot materials emit lightunder proper optical excitation and thus can be used as the fluorescentmaterials for systems and devices in this application. Morespecifically, semiconductor compounds such as, among others, CdSe andPbS, can be fabricated in form of particles with a diameter on the orderof the exciton Bohr radius of the compounds as quantum dot materials toemit light. To produce light of different colors, different quantum dotmaterials with different energy band gap structures may be used to emitdifferent colors under the same excitation light. Some quantum dots arebetween 2 and 10 nanometers in size and include approximately tens ofatoms such between 10 to 50 atoms. Quantum dots may be dispersed andmixed in various materials to form liquid solutions, powders, jelly-likematrix materials and solids (e.g., solid solutions). Quantum dot filmsor film stripes may be formed on a substrate as a screen for a system ordevice in this application. In one implementation, for example, threedifferent quantum dot materials can be designed and engineered to beoptically excited by the scanning laser beam as the optical pump toproduce light in red, green, and blue colors suitable for forming colorimages. Such quantum dots may be formed on the screen as pixel dotsarranged in parallel lines (e.g., repetitive sequential red pixel dotline, green pixel dot line and blue pixel dot line).

Examples of scanning beam display systems described here use at leastone scanning laser beam to excite color light-emitting materialsdeposited on a screen to produce color images. The scanning laser beamis modulated to carry images in red, green and blue colors or in othervisible colors and is controlled in such a way that the laser beamexcites the color light-emitting materials in red, green and blue colorswith images in red, green and blue colors, respectively. Hence, thescanning laser beam carries the images but does not directly produce thevisible light seen by a viewer. Instead, the color light-emittingfluorescent materials on the screen absorb the energy of the scanninglaser beam and emit visible light in red, green and blue or other colorsto generate actual color images seen by the viewer.

Laser excitation of the fluorescent materials using one or more laserbeams with energy sufficient to cause the fluorescent materials to emitlight or to luminesce is one of various forms of optical excitation. Inother implementations, the optical excitation may be generated by anon-laser light source that is sufficiently energetic to excite thefluorescent materials used in the screen. Examples of non-laserexcitation light sources include various light-emitting diodes (LEDs),light lamps and other light sources that produce light at a wavelengthor a spectral band to excite a fluorescent material that converts thelight of a higher energy into light of lower energy in the visiblerange. The excitation optical beam that excites a fluorescent materialon the screen can be at a frequency or in a spectral range that ishigher in frequency than the frequency of the emitted visible light bythe fluorescent material. Accordingly, the excitation optical beam maybe in the violet spectral range and the ultra violet (UV) spectralrange, e.g., wavelengths under 420 nm. In the examples described below,UV light or a UV laser beam is used as an example of the excitationlight for a phosphor material or other fluorescent material and may belight at other wavelength.

FIG. 1 illustrates an example of a laser-based display system using ascreen having color phosphor stripes. Alternatively, color pixilatedlight-emitting areas may also be used to define the image pixels on thescreen. The system includes a laser module 110 to produce and project atleast one scanning laser beam 120 onto a screen 101. The screen 101 hasparallel color phosphor stripes in the vertical direction and twoadjacent phosphor stripes are made of different phosphor materials thatemit light in different colors. In the illustrated example, red phosphorabsorbs the laser light to emit light in red, green phosphor absorbs thelaser light to emit light in green and blue phosphor absorbs the laserlight to emit light in blue. Adjacent three color phosphor stripes arein three different colors. One particular spatial color sequence of thestripes is shown in FIG. 1 as red, green and blue. Other color sequencesmay also be used. The laser beam 120 is at the wavelength within theoptical absorption bandwidth of the color phosphors and is usually at awavelength shorter than the visible blue and the green and red colorsfor the color images. As an example, the color phosphors may bephosphors that absorb UV light in the spectral range from about 380 nmto about 420 nm to produce desired red, green and blue light. The lasermodule 110 can include one or more lasers such as UV diode lasers toproduce the beam 120, a beam scanning mechanism to scan the beam 120horizontally and vertically to render one image frame at a time on thescreen 101, and a signal modulation mechanism to modulate the beam 120to carry the information for image channels for red, green and bluecolors. Such display systems may be configured as rear projectionsystems where the viewer and the laser module 110 are on the oppositesides of the screen 101. Alternatively, such display systems may beconfigured as front projection systems where the viewer and laser module110 are on the same side of the screen 101.

Examples of implementations of various features, modules and componentsin the scanning laser display system in FIG. 1 are described in U.S.patent application Ser. No. 10/578,038 entitled “Display Systems andDevices Having Screens With Optical Fluorescent Materials” and filed onMay 2, 2006 (U.S. patent Publication Ser. No. ______), PCT PatentApplication No. PCT/US2007/004004 entitled “Servo-Assisted Scanning BeamDisplay Systems Using Fluorescent Screens” and filed on Feb. 15, 2007(PCT Publication No. ______), PCT Patent Application No.PCT/US2007/068286 entitled “Phosphor Compositions For Scanning BeamDisplays” and filed on May 4, 2007 (PCT Publication No. ______), PCTPatent Application No. PCT/US2007/68989 entitled “MultilayeredFluorescent Screens for Scanning Beam Display Systems” and filed on May15, 2007 (PCT Publication No.), and PCT Patent Application No.PCT/US2006/041584 entitled “Optical Designs for Scanning Beam DisplaySystems Using Fluorescent Screens” and filed on Oct. 25, 2006 (PCTPublication No. WO 2007/050662). The disclosures of the above-referencedpatent applications are incorporated by reference in their entirety aspart of the specification of this application.

FIG. 2A shows an exemplary design of the screen 101 in FIG. 1. Thescreen 101 may include a rear substrate 201 which is transparent to thescanning laser beam 120 and faces the laser module 110 to receive thescanning laser beam 120. A second front substrate 202, is fixed relativeto the rear substrate 201 and faces the viewer in a rear projectionconfiguration. A color phosphor stripe layer 203 is placed between thesubstrates 201 and 202 and includes phosphor stripes. The color phosphorstripes for emitting red, green and blue colors are represented by “R”,“G” and “B,” respectively. The front substrate 202 is transparent to thered, green and blue colors emitted by the phosphor stripes. Thesubstrates 201 and 202 may be made of various materials, including glassor plastic panels. Each color pixel includes portions of three adjacentcolor phosphor stripes in the horizontal direction and its verticaldimension is defined by the beam spread of the laser beam 120 in thevertical direction. As such, each color pixel includes three subpixelsof three different colors (e.g., the red, green and blue). The lasermodule 110 scans the laser beam 120 one horizontal line at a time, e.g.,from left to right and from top to bottom to fill the screen 101. Thelaser module 110 is fixed in position relative to the screen 101 so thatthe scanning of the beam 120 can be controlled in a predetermined mannerto ensure proper alignment between the laser beam 120 and each pixelposition on the screen 101.

In FIG. 2A, the scanning laser beam 120 is directed at the greenphosphor stripe within a pixel to produce green light for that pixel.FIG. 2B further shows the operation of the screen 101 in a view alongthe direction B-B perpendicular to the surface of the screen 101. Sinceeach color stripe is longitudinal in shape, the cross section of thebeam 120 may be shaped to be elongated along the direction of the stripeto maximize the fill factor of the beam within each color stripe for apixel. This may be achieved by using a beam shaping optical element inthe laser module 110. A laser source that is used to produce a scanninglaser beam that excites a phosphor material on the screen may be asingle mode laser or a multimode laser. The laser may also be a singlemode along the direction perpendicular to the elongated directionphosphor stripes to have a small beam spread that is confined by thewidth of each phosphor stripe. Along the elongated direction of thephosphor stripes, this laser beam may have multiple modes to spread overa larger area than the beam spread in the direction across the phosphorstripe. This use of a laser beam with a single mode in one direction tohave a small beam footprint on the screen and multiple modes in theperpendicular direction to have a larger footprint on the screen allowsthe beam to be shaped to fit the elongated color subpixel on the screenand to provide sufficient laser power in the beam via the multimodes toensure sufficient brightness of the screen.

Referring now to FIG. 3, an example implementation of the laser module110 in FIG. 1 is illustrated. A laser array 310 with multiple lasers isused to generate multiple laser beams 312 to simultaneously scan thescreen 101 for enhanced display brightness. A signal modulationcontroller 320 is provided to control and modulate the lasers in thelaser array 310 so that the laser beams 312 are modulated to carry theimage to be displayed on the screen 101. The signal modulationcontroller 320 can include a digital image processor that generatesdigital image signals for the three different color channels and laserdriver circuits that produce laser control signals carrying the digitalimage signals. The laser control signals are then applied to modulatethe lasers, e.g., the currents for laser diodes, in the laser array 310.

The beam scanning can be achieved by using a scanning mirror 340 such asa galvo mirror for the vertical scanning and a multi-facet polygonscanner 350 for the horizontal scanning. A scan lens 360 can be used toproject the scanning beams form the polygon scanner 350 onto the screen101. The scan lens 360 is designed to image each laser in the laserarray 310 onto the screen 101. Each of the different reflective facetsof the polygon scanner 350 simultaneously scans N horizontal lines whereN is the number of lasers. In the illustrated example, the laser beamsare first directed to the galvo mirror 340 and then from the galvomirror 340 to the polygon scanner 350. The output scanning beams 120 arethen projected onto the screen 101. A relay optics module 330 is placedin the optical path of the laser beams 312 to modify the spatialproperty of the laser beams 312 and to produce a closely packed bundleof beams 332 for scanning by the galvo mirror 340 and the polygonscanner 350 as the scanning beams 120 projected onto the screen 101 toexcite the phosphors and to generate the images by colored light emittedby the phosphors. A relay optics module 370 is inserted between thescanners 340 and 350 to image the reflective surface of the reflector inthe vertical scanner 340 into a respective reflecting facet of thepolygon scanner 350 in order to prevent beam walk across the thin facetof the polygon scanner 350 in the vertical direction.

The laser beams 120 are scanned spatially across the screen 101 to hitdifferent color pixels at different times. Accordingly, each of themodulated beams 120 carries the image signals for the red, green andblue colors for each pixel at different times and for different pixelsat different times. Hence, the beams 120 are coded with imageinformation for different pixels at different times by the signalmodulation controller 320. The beam scanning thus maps the time-domaincoded image signals in the beams 120 onto the spatial pixels on thescreen 101. For example, the modulated laser beams 120 can have eachcolor pixel time equally divided into three sequential time slots forthe three color subpixels for the three different color channels. Themodulation of the beams 120 may use pulse modulation techniques toproduce desired grey scales in each color, a proper color combination ineach pixel, and desired image brightness.

In one implementation, the multiple beams 120 are directed onto thescreen 101 at different and adjacent vertical positions with twoadjacent beams being spaced from each other on the screen 101 by onehorizontal line of the screen 101 along the vertical direction. For agiven position of the galvo mirror 340 and a given position of thepolygon scanner 350, the beams 120 may not be aligned with each otheralong the vertical direction on the screen 101 and may be at differentpositions on the screen 101 along the horizontal direction. The beams120 can only cover one portion of the screen 101. At a fixed angularposition of the galvo mirror 340, the spinning of the polygon scanner350 causes the beams 120 from N lasers in the laser array 310 to scanone screen segment of N adjacent horizontal lines on the screen 101. Atthe end of each horizontal scan over one screen segment, the galvomirror 340 is adjusted to a different fixed angular position so that thevertical positions of all N beams 120 are adjusted to scan the nextadjacent screen segment of N horizontal lines. This process iteratesuntil the entire screen 101 is scanned to produce a full screen display.

In the above example of a scanning beam display system shown in FIG. 3,the scan lens 360 is located downstream from the beam scanning devices340 and 350 and focuses the one or more scanning excitation beams 120onto the screen 101. This optical configuration is referred to as a“pre-objective” scanning system. In such a pre-objective design, ascanning beam directed into the scan lens 360 is scanned along twoorthogonal directions. Therefore, the scan lens 360 is designed to focusthe scanning beam onto the screen 101 along two orthogonal directions.In order to achieve the proper focusing in both orthogonal directions,the scan lens 360 can be complex and, often, are made of multiples lenselements. In one implementation, for example, the scan lens 360 can be atwo-dimensional f-theta lens that is designed to have a linear relationbetween the location of the focal spot on the screen and the input scanangle (theta) when the input beam is scanned around each of twoorthogonal axes perpendicular to the optic axis of the scan lens. Thetwo-dimensional scan lens 360 such as a f-theta lens in thepre-objective configuration can exhibit optical distortions along thetwo orthogonal scanning directions which cause beam positions on thescreen 101 to trace a curved line. The scan lens 360 can be designedwith multiple lens elements to reduce the bow distortions and can beexpensive to fabricate.

To avoid the above distortion issues associated with a two-dimensionalscan lens in a pre-objective scanning beam system, a post-objectivescanning beam display system can be implemented to replace thetwo-dimensional scan lens 360 with a simpler, less expensive1-dimensional scan lens. U.S. patent application Ser. No. 11/742,014entitled “POST-OBJECTIVE SCANNING BEAM SYSTEMS” and filed on Apr. 30,2007 (U.S. patent Publication Ser. No. ______) describes examples ofpost-objective scanning beam systems suitable for use with phosphorscreens described in this application and is incorporated by referenceas part of the specification of this application.

FIG. 4 shows an example implementation of a post-objective scanning beamdisplay system based on the system design in FIG. 1. A laser array 310with multiple lasers is used to generate multiple laser beams 312 tosimultaneously scan a screen 101 for enhanced display brightness. Asignal modulation controller 320 is provided to control and modulate thelasers in the laser array 310 so that the laser beams 312 are modulatedto carry the image to be displayed on the screen 101. The beam scanningis based on a two-scanner design with a horizontal scanner such as apolygon scanner 350 and a vertical scanner such as a galvanometerscanner 340. Each of the different reflective facets of the polygonscanner 350 simultaneously scans N horizontal lines where N is thenumber of lasers. A relay optics module 330 reduces the spacing of laserbeams 312 to form a compact set of laser beams 332 that spread withinthe facet dimension of the polygon scanner 350 for the horizontalscanning. Downstream from the polygon scanner 350, there is a 1-Dhorizontal scan lens 380 followed by a vertical scanner 340 (e.g., agalvo mirror) that receives each horizontally scanned beam 332 from thepolygon scanner 350 through the 1-D scan lens 380 and provides thevertical scan on each horizontally scanned beam 332 at the end of eachhorizontal scan prior to the next horizontal scan by the next facet ofthe polygon scanner 350. The vertical scanner 340 directs the 2-Dscanning beams 390 to the screen 101.

Under this optical design of the horizontal and vertical scanning, the1-D scan lens 380 is placed downstream from the polygon scanner 140 andupstream from the vertical scanner 340 to focus each horizontal scannedbeam on the screen 101 and minimizes the horizontal bow distortion todisplayed images on the screen 101 within an acceptable range, thusproducing a visually “straight” horizontal scan line on the screen 101.Such a 1-D scan lens 380 capable of producing a straight horizontal scanline is relatively simpler and less expensive than a 2-D scan lens ofsimilar performance. Downstream from the scan lens 380, the verticalscanner 340 is a flat reflector and simply reflects the beam to thescreen 101 and scans vertically to place each horizontally scanned beamat different vertical positions on the screen 101 for scanning differenthorizontal lines. The dimension of the reflector on the vertical scanner340 along the horizontal direction is sufficiently large to cover thespatial extent of each scanning beam coming from the polygon scanner 350and the scan lens 380. The system in FIG. 4 is a post-objective designbecause the 1-D scan lens 380 is upstream from the vertical scanner 340.In this particular example, there is no lens or other focusing elementdownstream from the vertical scanner 340.

Notably, in the post-objective system in FIG. 4, the distance from thescan lens to a location on the screen 101 for a particular beam varieswith the vertical scanning position of the vertical scanner 340.Therefore, when the 1-D scan lens 380 is designed to have a fixed focaldistance along the straight horizontal line across the center of theelongated 1-D scan lens, the focal properties of each beam must changewith the vertical scanning position of the vertical scanner 380 tomaintain consistent beam focusing on the screen 101. In this regard, adynamic focusing mechanism can be implemented to adjust convergence ofthe beam going into the 1-D scan lens 380 based on the vertical scanningposition of the vertical scanner 340.

For example, in the optical path of the one or more laser beams from thelasers to the polygon scanner 350, a stationary lens and a dynamicrefocus lens can be used as the dynamic focusing mechanism. Each beam isfocused by the dynamic focus lens at a location upstream from thestationary lens. When the focal point of the lens coincides with thefocal point of the lens, the output light from the lens is collimated.Depending on the direction and amount of the deviation between the focalpoints of the lenses, the output light from the collimator lens towardthe polygon scanner 350 can be either divergent or convergent. Hence, asthe relative positions of the two lenses along their optic axis areadjusted, the focus of the scanned light on the screen 101 can beadjusted. A refocusing lens actuator can be used to adjust the relativeposition between the lenses in response to a control signal. In thisparticular example, the refocusing lens actuator is used to adjust theconvergence of the beam directed into the 1-D scan lens 380 along theoptical path from the polygon scanner 350 in synchronization with thevertical scanning of the vertical scanner 340. The vertical scanner 340in FIG. 4 scans at a much smaller rate than the scan rate of the firsthorizontal scanner 350 and thus a focusing variation caused by thevertical scanning on the screen 101 varies with time at the slowervertical scanning rate. This allows a focusing adjustment mechanism tobe implemented in the system of FIG. 1 with the lower limit of aresponse speed at the slower vertical scanning rate rather than the highhorizontal scanning rate.

The beams 120 on the screen 101 are located at different and adjacentvertical positions with two adjacent beams being spaced from each otheron the screen 101 by one horizontal line of the screen 101 along thevertical direction. For a given position of the galvo mirror 540 and agiven position of the polygon scanner 550, the beams 120 may not bealigned with each other along the vertical direction on the screen 101and may be at different positions on the screen 101 along the horizontaldirection. The beams 120 can cover one portion of the screen 101. At afixed angular position of the galvo mirror 540, the spinning of thepolygon scanner 550 causes the beams 120 from N lasers in the laserarray 510 to scan one screen segment of N adjacent horizontal lines onthe screen 101. At the end of each horizontal scan, the galvo mirror 540is adjusted to a different fixed angular position so that the verticalpositions of all N beams 120 are adjusted to scan the next adjacentscreen segment of N horizontal lines. This process iterates until theentire screen 101 is scanned to produce a full screen display.

FIG. 5 illustrates the above simultaneous scanning of one screen segmentwith multiple scanning laser beams 120 at a time. Visually, the beams120 behaves like a paint brush to “paint” one thick horizontal strokeacross the screen 101 at a time to cover one screen segment between thestart edge and the end edge of the image area of the screen 101 and thensubsequently to “paint” another thick horizontal stroke to cover anadjacent vertically shifted screen segment. Assuming the laser array 310has 36 lasers, a 1080-line progressive scan of the screen 101 wouldrequire scanning 30 vertical screen segments for a full scan. Hence,this configuration in an effect divides the screen 101 along thevertical direction into multiple screen segments so that the N scanningbeams scan one screen segment at a time with each scanning beam scanningonly one line in the screen segment and different beams scanningdifferent sequential lines in that screen segment. After one screensegment is scanned, the N scanning beams are moved at the same time toscan the next adjacent screen segment.

In the above design with multiple laser beams, each scanning laser beam120 scans only a number of lines across the entire screen along thevertical direction that is equal to the number of screen segments.Hence, the polygon scanner 550 for the horizontal scanning can operateat slower speeds than scanning speeds required for a single beam designwhere the single beam scans every line of the entire screen. For a givennumber of total horizontal lines on the screen (e.g., 1080 lines inHDTV), the number of screen segments decreases as the number of thelasers increases. Hence, with 36 lasers, the galvo mirror and thepolygon scanner scan 30 lines per frame while a total of 108 lines perframe are scanned when there are only 10 lasers. Therefore, the use ofthe multiple lasers can increase the image brightness which isapproximately proportional to the number of lasers used, and, at thesame time, can also advantageously reduce the response speeds of thescanning system.

A scanning display system described in this specification can becalibrated during the manufacture process so that the laser beam on-offtiming and position of the laser beam relative to the fluorescentstripes in the screen 101 are known and are controlled within apermissible tolerance margin in order for the system to properly operatewith specified image quality. However, the screen 101 and components inthe laser module 101 of the system can change over time due to variousfactors, such as scanning device jitter, changes in temperature orhumidity, changes in orientation of the system relative to gravity,settling due to vibration, aging and others. Such changes can affect thepositioning of the laser source relative to the screen 101 over time andthus the factory-set alignment can be altered due to such changes.Notably, such changes can produce visible and, often undesirable,effects on the displayed images. For example, a laser pulse in thescanning excitation beam 120 may hit a subpixel that is adjacent to anintended target subpixel for that laser pulse due to a misalignment ofthe scanning beam 120 relative to the screen along the horizontalscanning direction. When this occurs, the coloring of the displayedimage is changed from the intended coloring of the image. Hence, a redpixel in the intended image may be displayed as a green pixel on thescreen. For another example, a laser pulse in the scanning excitationbeam 120 may hit both the intended target subpixel and an adjacentsubpixel next to the intended target subpixel due to a misalignment ofthe scanning beam 120 relative to the screen along the horizontalscanning direction. When this occurs, the coloring of the displayedimage is changed from the intended coloring of the image and the imageresolution deteriorates. The visible effects of these changes canincrease as the screen display resolution increases because a smallerpixel means a smaller tolerance for a change in position. In addition,as the size of the screen increases, the effect of a change that canaffect the alignment can be more pronounced because a large moment armin scanning each excitation beam 120 associated with a large screenmeans that an angular error can lead to a large position error on thescreen. For example, if the laser beam position on the screen for aknown beam angle changes over time, the result is a color shift in theimage. This effect can be noticeable and thus undesirable to the viewer.

Implementations of various alignment mechanisms are provided in thisspecification to maintain proper alignment of the scanning beam 120 onthe desired sub-pixel to achieved desired image quality. These alignmentmechanisms include reference marks on the screen, both in thefluorescent area and in one or more peripheral area outside thefluorescent area, to provide feedback light that is caused by theexcitation beam 120 and represents the position and other properties ofthe scanning beam on the screen. The feedback light can be measured byusing one or more optical servo sensors to produce a feedback servosignal. A servo control in the laser module 110 processes this feedbackservo signal to extract the information on the beam positioning andother properties of the beam on the screen and, in response, adjust thedirection and other properties of the scanning beam 120 to ensure theproper operation of the display system.

For example, a feedback servo control system can be provided to useperipheral servo reference marks positioned outside the display areaunobservable by the viewer to provide control over various beamproperties, such as the horizontal positioning along the horizontalscanning direction perpendicular to the fluorescent stripes, thevertical positioning along the longitudinal direction of the fluorescentstripes, the beam focusing on the screen for control the imagesharpness, and the beam power on the screen for control the imagebrightness. For another example, a screen calibration procedure can beperformed at the startup of the display system to measure the beamposition information as a calibration map so having the exact positionsof sub-pixels on the screen in the time domain. This calibration map isthen used by the laser module 110 to control the timing and positioningof the scanning beam 120 to achieve the desired color purity. For yetanother example, a dynamic servo control system can be provided toregularly update the calibration map during the normal operation of thedisplay system by using servo reference marks in the fluorescent area ofthe screen to provide the feedback light without affecting the viewingexperience of a viewer.

Referring to FIG. 1, the laser module 110 also produces an invisibleservo beam 130 such as an IR beam and scans the servo beam 130 on to thescreen 101 along with the excitation beam 120. Different from theexcitation beam 120, the servo beam 130 is not modulated to carry imagedata. The servo beam 130 can be a CW beam. The stripe dividers on thescreen 101 can be made reflective to the light of the servo beam 130 andto produce feedback light 132 by reflection. The servo beam 130 has aknown spatial relation with the excitation beam 120. Therefore, thepositioning of the servo beam 130 can be used to determine thepositioning of the excitation beam 120. This relationship between theservo beam and excitation beams can be determined by using referenceservo marks such as a start of line mark in a non-viewing area of thescreen 101. The laser module 101 receives and detects the feedback light132 to obtain positioning information of the servo beam 130 on thescreen 101 and use this positioning information to control alignment ofthe excitation beam 120 on the screen. The servo beam 130 is invisibleand does not produce any noticeable visual artifact on the screen 101during the normal operation of the system when images are produced onthe screen 101. For example, the servo beam 130 can have a wavelength ina range from 780 nm to 820 nm. For safety concerns, the screen 101 canbe made to have a filter that blocks the invisible servo beam 130 fromexiting the screen 101 on the viewer side. In this regard, a cutoffabsorbing filter with a bandpass transmission range only in the visiblespectral range (e.g., from 420 nm to 680 nm) may be used to block theservo beam 130 and excitation beam 120. The servo control of theexcitation beam 120 based on the servo beam 130 can be performeddynamically during the normal operation of the system. This servo designavoids manipulation of the image-producing excitation beam 120 duringthe normal display mode for servo operations and thus avoids any visualartifacts that may be caused by the servo-related manipulation of theimage-producing excitation beam 120.

In addition, the scattered or reflected excitation light by the screen101 may also be used for servo control operations during a period whenthe system does not show images, e.g., during the startup period of thesystem or when the excitation beam 120 is outside the active displayarea of the screen 101. In such a case, the scattered or reflectedexcitation light, labeled as light 122, can be used as servo feedbacklight for servo control of the horizontal alignment of each laser.

In the examples of the systems in FIGS. 3 and 4, the servo beam 130 isdirected along with the one or more excitation beams 120 through thesame optical path that includes the relay optics module 330A or 330B,the beam scanners 340 and 350, and the scan lens 360 or 380. Referringto FIG. 5, the servo beam 130 is scanned along with the scanningexcitation beams 120 one screen segment at a time along the verticaldirection of the screen. The servo beam 130 is invisible and can beoverlapped with a scanning path of one excitation beam 120 or along itsown scanning path that is different from a path of any of the excitationbeams 120. The spatial relation between the servo beam 130 and eachexcitation beam 120 is known and fixed so that the positioning of theservo beam 130 on the screen 101 can be used to infer positioning ofeach excitation beam 120.

A light source for generating the servo beam 130 and a light source forgenerating an excitation beam 120 can be semiconductor lasers in a lightsource module which can be an array of lasers and at least one of thelasers in the laser array can be a servo laser that produces the servobeam 130. The location of the servo laser is known relative to eachexcitation laser. The servo beam 130 and each excitation beam 120 aredirected through the same relay optics, the same beam scanners and thesame projection lens and are projected on the screen 101. Therefore, thepositioning of the servo beam 130 on the screen 101 has a known relationwith the positioning of each excitation beam 120 on the screen. Thisrelation between the servo beam 130 and each excitation beam 120 can beused to control the excitation beam 120 based on measured positioning ofthe servo beam 130.

FIG. 5A shows a map of beam positions on the screen produced by a laserarray of thirty-six excitation lasers and one IR servo laser when avertical galvo scanner and a horizontal polygon scanner are at theirrespective null positions in a prototype pre-objective scanning displaysystem. The thirty-six excitation lasers are arranged in a 4×9 laserarray and the IR servo laser is placed in the center of the laser array.The laser beams occupy an area of about 20 mm×25 mm on the screen. Inthis example, the vertical spacing is one half of a pixel between twovertically adjacent excitation lasers and the horizontal spacing betweentwo adjacent excitation lasers is 3.54 pixels. Because the excitationlasers are spatially staggered along both horizontal and verticaldirections, each scan in one screen segment produces thirty-sixhorizontal lines on the screen occupying thirty-six pixels along thevertical direction. In operation, these thirty-seven laser beams arescanned together based on the scanning shown in FIG. 5 to scan onescreen segment at a time to sequentially scan different screen segmentsat different vertical positions to scan the entire screen. Because theIR servo laser is fixed in position with respect to each and every oneof the thirty-six excitation lasers, the positioning of the servo beam130 produced by the IR servo laser on the screen 101 has a knownrelation with respect to each beam spot of an excitation beam 120 fromeach of the thirty-six excitation lasers.

FIG. 6 illustrates a scanning beam display system based on a servocontrol using the invisible servo beam 130. A display processor andcontroller 640 can be used to provide control functions and controlintelligence based on servo detector signals from radiation servodetectors 620 that detect servo feedback light 132 from the screen 101.A single detector 620 may be sufficient and two or more servo detectors620 can be used to improve the servo detection sensitivity. Similarly,one or more radiation servo detectors 630 may also be used to collectexcitation servo light 122 produced by scattering or reflecting theexcitation beam 120 at the screen to provide additional feedback signalsto the processor and controller 640 for the servo control. A scanningprojection module 610 is provided to scan and project the excitation andservo beams 120 and 130 onto the screen. The module 610 can be in apost-objective configuration or a pre-objective configuration. Asillustrated, the image data is fed to the display processor andcontroller 640 which produces an image data signal carrying the imagedata to the signal modulator controller 520 for the excitation lasers510. The servo laser which is among the excitation lasers in the array510 is not modulated to carry image data. The signal modulationcontroller 520 can include laser driver circuits that produce lasermodulation signals carrying image signals with image data assigned todifferent lasers 510, respectively. The laser control signals are thenapplied to modulate the lasers in the laser array 510, e.g., thecurrents for laser diodes to produce the laser beams 512. The displayprocessor and controller 640 also produces laser control signals to thelasers in the laser array 510 to adjust the laser orientation to changethe vertical beam position on the screen 101 or the DC power level ofeach laser. The display processor and controller 5930 further producesscanning control signals to the scanning projection module 610 tocontrol and synchronize the horizontal polygon scanner and the verticalscanner.

FIG. 7 shows one example of the servo detector design where a servodetector 620 detects the servo feedback light 132. The servo detector620 can be a detector designed to be sensitive to light of the servobeam wavelength and less sensitive to visible light. An optical filter710 can be used to filter the light from the screen 101 to selectivelytransmit the servo feedback light 132 while blocking light at otherwavelengths, such as the excitation light and visible light. Such afilter allows a wider range of optical detectors to be used as the servodetector. FIG. 7 also shows an example of a servo detector 630 fordetecting the servo feedback light 122 at the excitation wavelength. Theservo detector 620 can be a detector designed to be sensitive to lightof the excitation wavelength of the excitation beam 120 and lesssensitive to light at wavelengths of the servo beam 130 and the visiblelight emitted by the screen 101. An optical filter 720 can be used tofilter the light from the screen 101 to selectively transmit theexcitation servo feedback light 122 while blocking light at otherwavelengths. The servo detector signals 721 and 722 from the servodetectors 620 and 630, respectively, are directed to the processor andcontroller 640 for servo control operations.

FIGS. 8 and 9 show two exemplary screen designs for the screen 101 forproviding the feedback light 122 and 132. In FIG. 8, each strip divider810 is made optically reflective to the servo and excitation beams sothe reflection can be used as the feedback light 132. The strip divider810 can also be made reflective and opaque to light to optically isolateadjacent light-emitting stripes to enhance contrast and to reduce crosstalk. The light-emitting stripes such phosphor stripes emitting red,green and blue light are less reflective to the servo and excitationbeams than the stripe dividers 810 so that the feedback light 132exhibits a spike every time the servo or excitation beams 130 passthrough a stripe divider 810. An absorbent black layer 820 can be coatedon each stripe divider on the viewer side to reduce glare of ambientlight to the viewer. FIG. 9 shows another screen design where areflective servo reference mark 910 is formed on the excitation side ofeach strip divider 901, e.g., a reflective stripe coating.

In each horizontal scan, the beam 120 or 130 scans across thelight-emitting stripes and the reflections produced by the stripedividers can be used to indicate horizontal positions of the stripedividers, spacing between two adjacent stripe dividers and horizontalpositions of the horizontally scanned beam 120 or 130. Therefore,reflections from the stripe dividers can be used for servo control ofthe horizontal alignment between the beam 120 and the light-emittingstrips.

FIG. 10 shows operation of the stripe dividers as alignment referencemarks. As the servo beam 120 or 130 is scanned horizontally across thescreen 101 and the light at the servo beam shows a low power when theservo beam 130 is at a light-emitting stripe and a high power when theservo beam is at a stripe divider. When the beam spot of the servo beam130 on the screen 101 is less than the width of one subpixel, the powerof the servo light shows a periodic pattern in each horizontal scanwhere the high power peak corresponds to a stripe divider. This patterncan be used to measure the position of the stripe dividers or the widthof each stripe divider based on clock cycles of a clocking signal in theprocessor and controller 640. This measured information is used toupdate a positioning map of each excitation beam 120 in the horizontalscan. When the beam spot of the servo beam 130 is greater than one widthof the subpixel but is less than one color pixel made up by threeadjacent subpixels, the power of the servo light 132 still shows aperiodic pattern in each horizontal scan where the high power peakcorresponds to one color pixel and thus can be used for servo control.

In addition to the stripe dividers as alignment reference marks on thescreen 101, additional alignment reference marks can be implemented todetermine the relative position of the beam and the screen and otherparameters of the excitation beam on the screen. For example, during ahorizontal scan of the excitation and servo beams across thelight-emitting stripes, a start of line mark can be provided for thesystem to determine the beginning of the active light-emitting displayarea of the screen 101 so that the signal modulation controller of thesystem can properly control the timing in delivering optical pulses totargeted pixels. An end of line mark can also be provided for the systemto determine the end of the active light-emitting display area of thescreen 101 during a horizontal scan. For another example, a verticalalignment referenced mark can be provided for the system to determinewhether the scanning beams are pointed to a proper vertical location onthe screen. Other examples for reference marks may be one or morereference marks for measuring the beam spot size on the screen and oneor more reference marks on the screen to measure the optical power ofthe excitation beam 120. Such reference marks can be placed a regionoutside the active fluorescent area of the screen 101, e.g., in one ormore peripheral regions of the active fluorescent screen area and areused for both excitation and servo beams.

FIG. 11 illustrates one example of a fluorescent screen 101 havingperipheral reference mark regions. The screen 101 includes a centralactive light-emitting display area 1100 with parallel fluorescentstripes for displaying images, two stripe peripheral reference markregions 1110 and 1120 that are parallel to the fluorescent stripes. Eachperipheral reference mark region can be used to provide variousreference marks for the screen 101. In some implementations, only theleft peripheral reference mark region 1110 is provided without thesecond region 1120 when the horizontal scan across the fluorescentstripes is directed from the left to the right of the area 1100.

Such a peripheral reference mark region on the screen 101 allows thescanning display system to monitor certain operating parameters of thesystem. Notably, because a reference mark in the peripheral referencemark region is outside the active display area 1100 of the screen 101, acorresponding servo feedback control function can be performed outsidethe duration during the display operation when the excitation beam isscanning through the active fluorescent display area 2600 to displayimage. Therefore, a dynamic servo operation can be implemented withoutinterfering with the display of the images to the viewer. In thisregard, each scan can include a CW mode period when an excitation beamsans through the peripheral referenced mark region for the dynamic servosensing and control and a display mode period when the modulation of theexcitation beam is turned on to produce image-carrying optical pulses asthe excitation beam sans through the active fluorescent display area1100. The servo beam 130 is not modulated to carry image data and thuscan be a CW beam with a constant beam power when incident onto thescreen 101. The power of the reflected servo light in the feedback light132 is modulated by the reference marks and stripe dividers and otherscreen pattern on the screen 101. The modulated power of the reflectedservo light can be used to measure the location of the servo beam 130 onthe screen 101.

FIG. 12 shows an example of a start of line (SOL) reference mark 1210 inthe left peripheral region 1110 in the screen 101. The SOL referencemark 1210 can be an optically reflective, diffusive or fluorescentstripe parallel to the fluorescent stripes in the active light-emittingregion 1100 of the screen 101. The SOL reference mark 1210 is fixed at aposition with a known distance from the first fluorescent stripe in theregion 1100. SOL patterns may be a single reflective stripe in someimplementations and may include multiple vertical lines with uniform orvariable spacing in other implementations. Multiple lines are selectedfor redundancy, increasing the signal to noise ratio, accuracy ofposition (time) measurement, and providing missing pulse detection.

In operation, the scanning excitation beam 120 is scanned from the leftto the right in the screen 101 by first scanning through the peripheralreference mark region 1110 and then through the active region 1100. Whenthe beam 120 is in the peripheral reference mark region 1110, the signalmodulation controller in the laser module 110 of the system sets thebeam 120 in a mode that ensures adequate sampling of information withoutcrosstalk (e.g. one beam at a time during one frame) When the scanningexcitation beam 120 scans through the SOL reference mark 1210, the lightreflected, scattered or emitted by the SOL reference mark 1210 due tothe illumination by the excitation beam 1210 can be measured at an SOLoptical detector located near the SOL reference mark 1210. The presenceof this signal indicates the location of the beam 120. The SOL opticaldetector can be fixed at a location in the region 1110 on the screen 101or off the screen 101. Therefore, the SOL reference mark 1210 can beused to allow for periodic alignment adjustment during the lifetime ofthe system.

When the pulse from the SOL 1210 detected is detected for a givenexcitation beam, the laser can be controlled to, after the delayrepresenting the time for scanning the beam from the SOL 1210 to theleft edge of the active display area 1100, operate in the image mode andcarry optical pulses with imaging data. The system then recalls apreviously measured value for the delay from SOL pulse to beginning ofthe image area 1100. This process can be implemented in each horizontalscan to ensure that each horizontal line starts the image area properlyand optical pulses in each horizontal scan are aligned to thelight-emitting stripes. The correction is made prior to painting theimage for that line in the area 1100 on the screen 101, so there is notime lag in displaying the images caused by the servo control. Thisallows for both high frequency (up to line scan rate) and low frequencyerrors to be corrected.

The servo beam 130 can be used to provide a positioning reference foreach excitation beam 120 for controlling both the timing for beginningimage-carrying pulses before the excitation beam enters the activelight-emitting area 1100 and during the normal display when theexcitation beam 120 scans in the active light-emitting region 1100. FIG.13 illustrates the detected signal power of the light at the servo beamwavelength in the feedback light 132 to show optical signals indicativeof positions of the SOL mark and stripe dividers on the screen 101. Theoptical peaks in the feedback light shown in FIGS. 13 and 14 areidealized as sharp square wave signals and are likely to have tailingand leading profiles shown in FIGS. 15-16. Such a pulse signal withtrailing and leading profiles can be converted into square wave likepulse signals by edge detection.

Similar to the SOL mark 1210, an end-of-line (EOL) reference mark can beimplemented on the opposite side of the screen 101, e.g., in theperipheral reference mark region 1120 in FIG. 11. The SOL mark is usedto ensure the proper alignment of the laser beam with the beginning ofthe image area. This does not ensure the proper alignment during theentire horizontal scan because the position errors can be present acrossthe screen. Implementing the EOL reference mark and an end-of-lineoptical detector in the region 1120 can be used to provide a linear, twopoint correction of laser beam position across the image area. FIG. 14illustrates the detected signal power of the light at the serve beamwavelength in the feedback light 132 to show optical signals indicativeof positions of the SOL mark, stripe dividers and EOL mark on the screen101

When both SOL and EOL marks are implemented, the laser is turned oncontinuously in a continuous wave (CW) mode prior to reaching the EOLsensor area. Once the EOL signal is detected, the laser can be returnedto image mode and timing (or scan speed) correction calculations aremade based on the time difference between the SOL and EOL pulses. Thesecorrections are applied to the next one or more lines. Multiple lines ofSOL to EOL time measurements can be averaged to reduce noise.

Based on the stripe divider and SOL/EOL peripheral reference marks, thepositioning of the servo beam 130 on the screen 101 can be measured.Because the servo beam 130 has a fixed relation with each excitationbeam 120, any error in the positioning of the servo beam 130 suggests ancorresponding error in each excitation beam 120. Therefore, thepositioning information of the servo beam 130 can be used in the servocontrol to control the servo beam 130 and each excitation beam 120 toreduce an alignment error of the excitation beam.

The present servo control operates to place each optical pulse in theexcitation beam 120 near or at the center of a target light-emittingstripe to excite the light-emitting material in that stripe withoutspilling over to an adjacent light-emitting stripe. The servo controlcan be designed to achieve such alignment control by controlling thetiming of each optical pulse in order to place the pulse at a desiredposition on the screen 101 during a horizontal scan. Accordingly, theservo control, i.e., the processor and controller 640, needs to “know”horizontal positions of the light-emitting stripes in each horizontalline before each horizontal scan in order to control the timing ofoptical pulses during the scan. This information on horizontal positionsof the light-emitting stripes in each horizontal line constitutes atwo-dimensional position “map” of the active display area orlight-emitting area of the screen 101 of (x, y) coordinates where x isthe horizontal position of each stripe divider (or equivalently, thehorizontal position of the center of each stripe) and y is the verticalposition or ID number of a horizontal scan. This position map of thescreen 101 can be measured at the factory and may change in time due tochanges in the system components due to temperature, aging and otherfactors. For example, thermal expansion effects, and distortions in theoptical imaging system will need corresponding adjustments in theprecise timing to activate each color in a pixel. If the laser actuationdoes not properly correspond to the timing where the beam is directed atthe central portion of a sub-pixel or stripe for the intended phosphor,the beam 120 will either partially or completely activate the wrongcolor phosphor. In addition, this position map of the screen 101 canvary from one system to another due to the component and devicetolerances during the manufacturing.

Therefore, it is desirable to update the position map of the screen 101and to use the updated position map for controlling the timing of pulsesof the excitation beam 120 in each horizontal scan during the normaldisplay. The position map of the screen 101 can be obtained using thefeedback light 122 and 132 in a calibration scanning when the system isnot in the normal display mode, e.g., during the start-up phase of thesystem. In addition, the servo feedback light 132 can be used in realtime video display to monitor and measure changes in an existingposition map of the screen 101 when the system is operating in thenormal display mode to produce images on the screen 101. This mode ofthe servo control is referred to as dynamic servo. The dynamicmonitoring of the screen 101 can be useful when the system operates foran extended period time without a downtime because the screen 101 mayundergo changes that can lead to significant changes to the position mapof the screen 101 that is updated during the start-up phase of thesystem.

The position map of the screen 101 can be stored in the memory of thelaser module 110 and reused for an interval of time if the effects thatare being compensated for do not change significantly. In oneimplementation, when the display system is turned on, the display systemcan be configured to, as a default, set the timing of the laser pulsesof the scanning laser beam based on the data in the stored position map.The servo control can operate to provide the real-time monitoring usingthe servo feedback light 132 and to control the pulse timing during theoperation.

In another implementation, when the display system is turned on, thedisplay system can be configured to, as a default, to perform acalibration using the excitation beam 120 and the servo beam 130 to scanthrough the entire screen 101. The measured position data are used toupdate the position map of the screen 101. After this initialcalibration during the start-up phase, the system can be switched intothe normal display mode and, subsequently during the normal displayoperation, only the servo beam 130 is used to monitor the screen 101 andthe data on the screen 101 obtained from the servo beam 130 can be usedto dynamically update the position map and thus to control the timing ofpulses in the beam 130 in each horizontal scan.

The calibration of the position map of the screen 101 can be obtained byoperating each scanning beam 120 or 130 in a continuous wave (CW) modefor one frame during which the scanning laser beams 120 and 130simultaneously scan through the entire screen, one segment at a time asshown in FIG. 5, when multiple laser beams 120 are used. If a singlelaser is used to produce one excitation beam 120, the single scanningbeam 120 is set in the CW mode to scan the entire screen 101, one lineat a time, along with the servo beam 130. The feedback light 122 and 132from the servo reference marks on the stripe dividers is used to measurethe laser position on the screen 101 by using the servo detectors 620and 630.

The servo detector signals from the servo detectors 620 and 630 can besent through an electronic “peak” detector that creates an electronicpulse whenever a servo signal is at its highest relative amplitude. Thetime between these pulses can be measured by a sampling clock in adigital circuit or microcontroller that is used by the processor andcontroller 640 to process and generate an error signal for controllingtiming of optical pulses in each excitation beam 120 in a horizontalscan. Because the scan speed of the scanning beam 120 or 130 on thescreen 101 is known, the time between two adjacent pulses from theelectronic peak detector can be used to determine the spacing of the twolocations that produce the two adjacent electronic pulses. This spacingcan be used to determine the subpixel width and subpixel position.Depending on the beam scan rate and the frequency of the sampling clock,there are some nominal number of clocks for each sub-pixel. Due tooptical distortions, screen defects or combination of the distortionsand defects, the number of clock cycles between two adjacent pulses forany given sub-pixel may vary from the nominal number of clock cycles.This variation in clock cycles can be encoded and stored in memory foreach sub-pixel.

FIG. 15 shows one example of the detected reflected feedback light as afunction of the scan time for a portion of one horizontal scan, therespective output of the peak detector and the sampling clock signal. Anominal subpixel with a width corresponding to 9 clock cycles of thesampling clock and an adjacent short subpixel corresponding to 8 clockcycles are illustrated. In some implementations, the width of a subpixelmay correspond to 10-20 clock cycles. The clock cycle of the samplingclock signal of the digital circuit or microcontroller for the servocontrol dictates the spatial resolution of the error signal.

FIG. 16 shows one example of the detected reflected feedback light as afunction of the scan time for a portion of one horizontal scan, therespective output of the peak detector and the sampling clock signalwhere a nominal subpixel corresponding to a width of 9 clock cycles andan adjacent long subpixel a corresponding to a width of 10 clock cyclesre illustrated.

During calibration, contaminants such as dust on the screen, screendefects, or some other factors may cause missing of an optical pulse inthe reflected feedback light that would have been generated by a servoreference mark between two adjacent subpixels on the screen 101. FIG. 17illustrates an example where a pulse is missing. A missing pulse can bedetermined if a pulse is not sampled or detected within the nominalnumber of clock cycles for a subpixel within the maximum expecteddeviation from the nominal number of clocks for a subpixel. If a pulseis missed, the nominal value of clock cycles for a subpixel can beassumed for that missing sub-pixel and the next sub-pixel can containthe timing correction for both sub-pixels. The timing correction can beaveraged over both sub-pixels to improve the detection accuracy. Thismethod may be extended for any number of consecutive missed pulses.

The above use of the sampling clock signal to measure the position mapof the screen 101 can be used with detection with the excitation servofeedback light 122 or the servo feedback light 132 from the screen 101.Because the excitation beam or beams 120 scan all horizontal lines inthe screen 101 during a calibration scan in a CW mode, the position datafrom the excitation servo feedback light 122 can provide data for eachand every subpixel of the screen 101. The position data obtained fromthe servo beam 130 and its corresponding feedback light 132, however,only covers one horizontal scan line per screen segment as shown in FIG.5. The position data measured from the servo beam 130 for one screensegment can be used as a representative scan for all horizontal lines inthat screen segment is used to update position data for all lines inthat screen segment. Two or more servo beams 130 may be used to increasethe number of lines measured in each screen segment.

Vertical position of each laser can be monitored and adjusted by usingan actuator, a vertical scanner, an adjustable lens in the optical pathof each laser beam or a combination of these and other mechanisms.Vertical reference marks can be provided on the screen to allow for avertical servo feedback from the screen to the laser module. One or morereflective, fluorescent or transmissive vertical reference marks can beprovided adjacent to the image area of the screen 101 to measure thevertical position of each excitation beam 120. Referring to FIG. 11,such vertical reference marks can be placed in a peripheral referencemark region. One or more vertical mark optical detectors can be used tomeasure the reflected, fluorescent or transmitted light from a verticalreference mark when illuminated by the beam 120 or 130. The output ofeach vertical mark optical detector is processed and the information onthe beam vertical position is used to control an actuator to adjust thevertical beam position on the screen 101.

FIG. 18A shows an example of a vertical reference mark 2810. The mark2810 includes is a pair of identical triangle reference marks 2811 and2812 that are separated and spaced from each other in both vertical andhorizontal directions to maintain an overlap along the horizontaldirection. Each triangle reference mark 2811 or 2812 is oriented tocreate a variation in the area along the vertical direction so that thebeam 120 partially overlaps with each mark when scanning through themark along the horizontal direction. As the vertical position of thebeam 120 changes, the overlapping area on the mark with the beam 120changes in size. The relative positions of the two marks 2811 and 2812defines a predetermined vertical beam position and the scanning beamalong a horizontal line across this predetermined vertical positionscans through the equal areas as indicated by the shadowed areas in thetwo marks 2811 and 2812. When the beam position is above thispredetermined vertical beam position, the beam sees a bigger mark areain the first mark 2811 than the mark area in the second mark 2812 andthis difference in the mark areas seen by the beam increases as the beamposition moves further up along the vertical direction. Conversely, whenthe beam position is below this predetermined vertical beam position,the beam sees a bigger mark area in the second mark 2812 than the markarea in the first mark 2811 and this difference in the mark areas seenby the beam increases as the beam position moves further down along thevertical direction.

The feedback light from each triangle mark is integrated over the markand the integrated signals of the two marks are compared to produce adifferential signal. The sign of the differential signal indicated thedirection of the offset from the predetermined vertical beam positionand the magnitude of the differential signal indicates the amount of theoffset. The excitation beam is at the proper vertical position when theintegrated light from each triangle is equal, i.e., the differentialsignal is zero.

FIG. 18B shows a portion of the signal processing circuit as part of thevertical beam position servo feedback control in the laser module 110for the vertical reference mark in FIG. 18A. A PIN diode preamplifier2910 receives and amplifies the differential signal for the tworeflected signals from the two marks 2811 and 2812 and directs theamplified differential signal to an integrator 2920. Ananalog-to-digital converter 2930 is provided to convert the differentialsignal into a digital signal. A digital processor 2940 processes thedifferential signal to determine the amount and direction of theadjustment in the vertical beam position and accordingly produces avertical actuator control signal. This control signal is converted intoan analog control signal by a digital to analog converter 2950 and isapplied to a vertical actuator controller 2960 which adjusts theactuator. FIG. 18C further shows generation of the differential signalby using a single optical detector.

FIG. 19 shows an example of the screen in FIG. 11 having the start ofline reference mark and the vertical beam position reference marks.Multiple vertical beam position reference marks can be placed atdifferent vertical positions to provide vertical position sensing of theexcitation beams 120 in all screen segments. In addition, separate fromthe vertical beam position reference marks for the excitation beams 120,multiple vertical beam position reference marks can be placed atdifferent vertical positions, e.g., one vertical reference mark for theservo beam 130 to provide vertical position sensing of the servo beam130 in each screen segment. These vertical reference marks are presentedby the numeral “1910” in FIG. 19. The combination of the SOL reference1210, the vertical reference marks 1910 and the periodic pattern in thestrip stricture of the light-emitting area 1110 provides positioninginformation of the invisible servo beam 130, positioning information ofthe excitation beams 120 and the horizontal parameters of the pixels onthe screen 101 for servo control in a scanning display system.

FIG. 20 shows an example of the operation of a servo control using theservo beam 130 during the normal display mode when each excitation beam120 is used for carrying optical pulses for producing images on thescreen 101 and is not used for servo control. The servo beam 130 is a CWbeam and is scanned over one horizontal line per screen segment with thescanning modulated excitation Laser beams 120. The servo Feedback light132 is detected by the one or more servo detectors 620 to measure analignment error of the servo beam 130 on the screen 101 during thenormal display. The alignment of each excitation laser beam 120 isadjusted based on the measured alignment error of the servo beam 130 toreduce the alignment error of the excitation laser beam 120.

While this specification contains many specifics, these should not beconstrued as limitations on the scope of an invention or of what may beclaimed, but rather as descriptions of features specific to particularembodiments of the invention. Certain features that are described inthis specification in the context of separate embodiments can also beimplemented in combination in a single embodiment. Conversely, variousfeatures that are described in the context of a single embodiment canalso be implemented in multiple embodiments separately or in anysuitable subcombination. Moreover, although features may be describedabove as acting in certain combinations and even initially claimed assuch, one or more features from a claimed combination can in some casesbe excised from the combination, and the claimed combination may bedirected to a subcombination or a variation of a subcombination.

Only a few implementations are disclosed. However, it is understood thatvariations and enhancements may be made.

1. A scanning beam display system, comprising: an excitation light source to produce at least one excitation beam having optical pulses that carry image information; a servo light source to produce at least one servo beam at a servo beam wavelength that is invisible; a beam scanning module to receive the excitation beam and the servo beam and to scan the excitation beam and the servo beam; a light-emitting screen positioned to receive the scanning excitation beam and the servo beam and comprising a light-emitting area which comprises (1) parallel light-emitting stripes which absorb light of the excitation beam to emit visible light to produce images carried by the scanning excitation beam, and (2) stripe dividers parallel to and spatially interleaved with the light-emitting stripes with each stripe divider being located between two adjacent stripes, each stripe divider being optically reflective; an optical servo sensor positioned to receive light of the servo beam scanning on the screen including light reflected by the stripe dividers and to produce a monitor signal indicative of positioning of the servo beam on the screen; and a control unit operable to, in response to the positioning of the servo beam on the screen in the monitor signal, adjust timing of the optical pulses carried by the scanning excitation beam based on a relation between the servo beam and the excitation beam to control the spatial alignment of spatial positions of the optical pulses in the excitation beam on the screen.
 2. The system as in claim 1, wherein: the servo beam wavelength is greater than each wavelength in a visible spectral range of the visible light emitted by the light-emitting stripes.
 3. The system as in claim 1, wherein: the servo beam and the excitation beam co-propagate along a common optical path from the beam scanning module to the screen.
 4. The system as in claim 1, wherein: the screen comprises a reflective stripe line as a start of line servo reference mark outside the light-emitting area of the screen and parallel to the light-emitting stripes to indicate a reference position of the servo beam and a reference position of the excitation beam during a beginning of a beam scan of the servo beam or the horizontal beam perpendicular to the light-emitting stripes, and the control unit is operable to, based on received light of the servo beam from the start of line servo reference mark and the stripe dividers, to control the spatial alignment of spatial positions of the optical pulses in the excitation beam on the screen, when the excitation beam scans in the light-emitting area and produces the images.
 5. The system as in claim 4, wherein: the screen comprises a vertical beam position servo reference mark outside the light-emitting area in a beam scanning path perpendicular to the light-emitting stripes, the vertical beam position servo reference mark producing a vertical beam position servo feedback light when illuminated by the scanning beam to indicate information on a vertical beam position in a vertical direction parallel to the light-emitting stripes.
 6. The system as in claim 5, wherein: the a vertical beam position servo reference mark comprises first and second servo marks separated from each other along the beam scanning path.
 7. The system as in claim 1, wherein: the beam scanning module includes two beam scanners to scan the excitation and servo beams along two orthogonal directions and a projection lens downstream from the two beam scanners to project the scanning excitation and servo beams onto the screen.
 8. The system as in claim 1, wherein: the beam scanning module includes two beam scanners to scan the excitation and servo beams along two orthogonal directions and a projection lens located along an optical path between the two beam scanners to project the scanning excitation and servo beams onto the screen.
 9. The system as in claim 1, wherein: the optical servo sensor comprises a first optical photodetector responsive to light of the servo beam to produce a detector signal for received light of the servo beam.
 10. The system as in claim 1, wherein: the optical servo sensor comprises a first optical photodetector and a first optical filter to filter light entering into the first photodetector to allow passage of the light of the servo beam into the first optical photodetector while rejecting light of the at least one excitation beam.
 11. The system as in claim 1, wherein: the optical servo sensor comprises: a first optical photodetector and a first optical filter to filter light entering into the first photodetector to allow passage of the light of the servo beam into the first optical photodetector while rejecting light of the at least one excitation beam; and a second optical photodetector and a second optical filter to filter light entering into the second photodetector to allow passage of the light of the at least one excitation beam into the second optical photodetector while rejecting light of the servo beam.
 12. The system as in claim 11, wherein: the screen comprises a reflective stripe line as a start of line servo reference mark outside the light-emitting area of the screen and parallel to the light-emitting stripes to indicate a reference position of the servo beam and a reference position of the excitation beam, and the control unit is operable to, based on received light of the servo beam and the at least one excitation beam from the start of line servo reference mark from the first and second photodetectors, to determine a relative position between the servo beam and the at least one excitation beam, and to control the spatial alignment of spatial positions of the optical pulses in the excitation beam on the screen.
 13. The system as in claim 1, wherein: the screen comprises a filter located on one side of the screen opposite to a side that faces the excitation light source, the filter operable to transmit the visible light and to block light of the servo beam.
 14. A method for controlling a scanning beam display system, comprising: scanning at least one excitation beam modulated with optical pulses on a screen with parallel light-emitting stripes in a beam scanning direction perpendicular to the light-emitting stripes to excite the fluorescent strips to emit visible light which forms images, wherein the screen comprises stripe dividers parallel to and spatially interleaved with the light-emitting stripes with each stripe divider being located between two adjacent stripes and each stripe divider is optically reflective; scanning a servo beam, which is invisible, along with the excitation beam on the screen; detecting light of the scanning servo beam from the screen including light produced by the stripe dividers to obtain a monitor signal indicative of positioning of the servo beam on the screen; and in response to the positioning of the servo beam on the screen, adjusting timing of the optical pulses carried by the scanning excitation beam based on a relation between the servo beam and the excitation beam to control the spatial alignment of spatial positions of the optical pulses in the excitation beam on the screen.
 15. The method as in claim 14, comprising: prior to scanning the at least one excitation beam modulated with optical pulses to display images on the screen, performing a calibration scan to: scanning the least one excitation beam in a continuous wave mode to scan over the entire screen; detecting reflected excitation light from the stripe dividers to measure peak reflected signals corresponding to the stripe dividers; processing the reflected excitation light to extract pixel information of pixels on the screen; and using the extracted pixel information of pixels on the screen to control timing of optical pulses in subsequent scanning of the at least one excitation beam modulated with optical pulses to display images on the screen, wherein the positioning of the servo beam on the screen is used to modify timing of the optical pulses set by using the extracted pixel information of pixels on the screen.
 16. The method as in claim 14, wherein: the screen comprises a reflective stripe line as a start of line servo reference mark outside an area of the screen having the light-emitting stripes, the reflective stripe line being parallel to the light-emitting stripes to indicate a reference position of the servo beam and a reference position of the excitation beam s, and the method comprising: detecting light of the servo beam and the at least one excitation beam from the start of line servo reference mark, to determine a relative position between the servo beam and the at least one excitation beam, and to control the spatial alignment of spatial positions of the optical pulses in the excitation beam on the screen.
 17. The method as in claim 14, comprising: using a vertical beam position reference mark on the screen that is located outside an area having the parallel light-emitting stripes to reflect light of the at least one excitation beam; measuring the reflected light from the beam position reference mark to detect a vertical alignment error of the at least one excitation beam; and adjusting the at least one excitation beam to reduce the vertical alignment error.
 18. The method as in claim 14, comprising: using a vertical beam position reference mark on the screen that is located outside an area having the parallel light-emitting stripes to reflect light of the servo beam; measuring the reflected light from the beam position reference mark to detect a vertical alignment error of the servo beam; and adjusting the servo beam to reduce the vertical alignment error.
 19. A scanning beam display system, comprising: a light-emitting screen comprising a light-emitting area which comprises (1) parallel light-emitting stripes which absorb excitation light to emit visible light, and (2) optically reflective stripe dividers parallel to and spatially interleaved with the light-emitting stripes with each stripe divider being located between two adjacent stripes; a plurality of excitation lasers to produce excitation laser beams of the excitation light; at least one servo light source fixed in position relative to the excitation lasers to produce at least one servo beam at a servo beam wavelength that is invisible; a beam scanning module to receive the excitation laser beams and the servo beam and to scan the excitation laser beams and the servo beam; at least one first optical servo sensor positioned to receive light of the servo beam reflected from the screen to produce a first monitor signal indicative of positioning of the servo beam on the screen; at least one second optical servo sensor positioned to receive light of the excitation laser beams reflected from the screen to produce a second monitor signal indicative of positioning of each excitation laser beam on the screen; and a control unit operable to, in response to the first and the second monitor signals, adjust timing of the optical pulses carried by each excitation laser beam based on a relation between the servo beam and each excitation laser beam to control the spatial alignment of spatial positions of the optical pulses in the excitation beam on the screen.
 20. The system as in claim 19, wherein: the screen comprises a reflective stripe line as a start of line servo reference mark outside the light-emitting area of the screen and parallel to the light-emitting stripes to indicate a reference position of the servo beam and a reference position of each excitation laser beam, and the control unit is operable to, based on received light of the servo beam and each excitation laser beam from the start of line servo reference mark, to determine a relative position between the servo beam and each excitation laser beam, and to control the spatial alignment of spatial positions of the optical pulses in the excitation beam on the screen. 